a movement of the earth's crust, caused by some internal convulsion. Three kinds of earthquake movements are generally recognized. These are the wave movement, the vertical movement and the circular, or twisting, movement. The first is the most common and extends over the largest areas. The wave movement begins at a center, from which it moves in all directions, like a wave started by dropping a pebble into a pool of water. The earthquake wave, however, differs from the water wave in this: the irregular resistance which it receives from the different layers of rock prevents its moving in a circle, so that its outline soon becomes very irregular. The velocity is very great, often reaching thirty or forty miles a minute. These waves also move more rapidly in hard, elastic rock than in loose gravel or sand. The vertical movement acts like the explosion of a mine and usually throws masses of earth and rock into the air. The circular or twisting movement is the most destructive of all but it is happily of least frequent occurrence and is confined to very small areas. The causes of earthquakes are not well understood. Those in volcanic regions are evidently connected with volcanic action, and some are known to be caused by the eruptions which they precede; but those movements more or less remote from volcanic regions and extending over comparatively large areas, such as the earthquake at Charleston, S. C., in 1886, cannot logically be accounted for in this way. The most generally accepted view as to the cause of this sort of earthquake is that the movement of the earth's crust is caused by the contractions of cooling matter in the interior. When the motion is violent and rapid, the destructive effects of an earthquake are very great. An upward movement of a quarter of an inch will crack brick walls, and one of half an inch will shatter them. When occurring on or near the seacoast, earthquakes often cause great destruction and loss of life by the unusually high waves which they produce in the sea. These roll inland and flood regions that under ordinary conditions are entirely free from the action of the sea. Sometimes large steamers are carried from their moorings and left upon dry land, buildings are destroyed, basins are flooded and hundreds of people are drowned. In some localities changes of level are produced by earthquakes, courses of streams are altered, springs are dried up and new springs are formed. Fortunately, most shocks are mild, and those of a severe nature seldom occur. The most noted earthquake in the world's history are those at Lima in 1746; Lisbon in 1755, which caused the death of from 40,000 to 50,000 persons; Calabria in 1857; in Ecuador and Peru in 1868; at Charleston, S. C., in 1886; in Italy in 1887, and in Japan in 1891. The most destructive earthquake in the United States occurred in San Francisco and its immediate vicinity April 18, 1906. A large portion of the business part of the city was destroyed or so damaged as to make rebuilding necessary. The destructive effects extended for 125 miles north and 80 miles south of the city. Several buildings of the Leland Stanford University were damaged or destroyed. On August 16, 1906, several shocks occurred in South America. Valparaiso, Chili, suftered serious damage and loss of life. Santiago and other towns in the vicinity were also more or less affected. The greatest earthquake calamity known to history occurred in Calabria, Italy, and the island of Sicily on the morning of Dec. 28, 1908. The cities of Messina, with a population of 100,000, and Reggio, with a population of 50,000, were destroyed, together with twenty or more smaller towns along the coasts of Calabria and Sicily. The loss of life was estimated at from 120,000 to 150,000. The nations of Europe and the United States were prompt in their responses for relief, the Congress of the United States appropriating $800,000 from the national treasury. This was supplemented by private donations, and over $3,000,000 were contributed from this country. The cause of this earthquake is supposed to be a landslip or fault break (See FAULT).